Your statement was incorrect. The "arc" went from near Pakistan to the southern Indian Ocean.
And no...it could have evaded the military radar in Afghanistan if it had gone into Pakistan. Its very mountainous there and you can't see through the mountains. At just .5 degree elevation....and at 100 nm away....anything below 10K feet is not seen. Make that 200nm and you can fly at 30K feet and not be seen.
And that isn't including any beam blocking by the mountains...that's if it were over the ocean. The curve of the earth ensures stealth.
And if China knew that 150 of its citizens were being held captive in Pakistan there would be a Chinese armada heading that way.